Residual bond between concrete and reinforcing GFRP rebars at elevated temperatures

The use of glass-fibre-reinforced-polymer reinforcing bars instead of steel reinforcing bars is one of many ways to enhance the corrosion resistance of reinforced concrete structures. Fire performance of concrete members reinforced with fibreglass bars is a critical area that needs studying prior to using such bars in buildings and other structures vulnerable to fires. The mechanical properties of concrete and fibreglass as well as the bond between them can significantly deteriorate at high temperatures. The variations in bonding behaviour can affect the moment capacity of the structure, so it is necessary to know the bond strength degradation for structural design of fire safety and structural repair after fire. However, examination of bonding between fibreglass and concrete at elevated temperatures is quite challenging in practice and it needs a well-equipped experimental laboratory. In this study, fibreglass and concrete bond constitutive relationships are established for reinforced concrete subjected to fire. They are developed for the following purposes at high temperatures: to establish the compressive strength of concrete, ultimate tensile strength and modulus of elasticity of reinforcing bars, bond strength, slip at peak bond stress and bond stress-slip curve. The proposed relationships at elevated temperature are compared with experimental results.